New apparatus for measuring the drainage properties of unbound aggregates

摘要

This paper presents a new apparatus for the determination of 1-dimensional permeability as well as in-situ 3-dimensional permeability of unbound base course materials. The apparatus is based on the falling-head principle which has the advantage of being able to determine the permeability properties of test materials at different levels of hydraulic gradients in a single test. This new method also has further advantages of being fast and simple to use, and it is easy to convert the apparatus to a constant-head mode as well. The principle employed is to fit highly repeatable falling head test data to an exponential flow law as: v = ki~m, where k describes the permeability, and m the flow index, with m = 1 representing laminar flow, and m = 0.5 representing turbulent flow. To illustrate the characteristics of this equipment, this paper presents the results of permeability tests conducted on test specimens of approximately one-sized unbound aggregates and glass spheres. The results had excellent agreement with those obtained from constant-head tests on the same specimens. The proposed apparatus can be an effective tool for determining the drainage properties of unbound base materials within the range of hydraulic gradients encountered in actual road pavements.